naveenium
if you're just getting started and you aim to keep it light, then i'd start with the withings scale. you leave it in your bathroom, set your goals, step on it when you feel like it and watch trends and alerts from time to time. i find my weight tells me more about me over time than many other metrics: it shows my bad weeks from my good and, in indirect ways, shows when i stress out and get bad sleep (and therefore, end up eating poorly and exercising inconsistently)
this is why i believe a smart scale is one of the best examples of good data tracking: you step on it whenever you think of it (not on some weird schedule; nor do you have to wear it or take it with you). it does the mundane stuff of capturing the data and sending it to the cloud, which you would otherwise have to write into some notebook.
if it's a system that's fully automated though, one might lose interest in collecting it in the first place: the QSers always like to say – when you add a little friction to a process, you end up paying more attention to why it is. so instead of just blinding capturing your weight, setting up alerts for goals and seeing trends fall and rise will get you to make the most of the data – instead of just collecting data for data's sake.
you could probably do it today without the use of a private account
i believe in app settings, you can restrict the visibility of posts by any particular app. this way, your scale's posts could be seen by just you and not your friends.
thanks for the book recommendation - i will check it out this weekend!